40 lines
1.2 KiB
Markdown
40 lines
1.2 KiB
Markdown
[hidden.friends]
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# 16 Library introduction [[library]](./#library)
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## 16.4 Library-wide requirements [[requirements]](requirements#hidden.friends)
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### 16.4.6 Conforming implementations [[conforming]](conforming#hidden.friends)
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#### 16.4.6.6 Friend functions [hidden.friends]
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[1](#1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L3709)
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Whenever this document specifies
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a friend declaration of a function or function template
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within a class or class template definition,
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that declaration shall be
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the only declaration of that function or function template
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provided by an implementation[.](#1.sentence-1)
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[*Note [1](#note-1)*:
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In particular,
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a conforming implementation does not provide
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any additional declarations of that function or function template
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at namespace scope[.](#1.sentence-2)
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â *end note*]
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[*Note [2](#note-2)*:
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Such a friend function or function template declaration
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is known as a hidden friend,
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as it is visible neither
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to ordinary unqualified lookup ([[basic.lookup.unqual]](basic.lookup.unqual "6.5.3 Unqualified name lookup")) nor
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to qualified lookup ([[basic.lookup.qual]](basic.lookup.qual "6.5.5 Qualified name lookup"))[.](#1.sentence-3)
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â *end note*]
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